The disclosure came in a work order posted on a Web site controlled by the Ministry of National Defense (MND), which is having the fences strengthened after cattle were found roaming the facility, located in Linkou in the island’s northwest.

“The Defense Ministry’s Linyuan base covers a large area and has a long but insufficiently high perimeter fence. In several places, the fence has toppled over or is leaning, with cows breaching the perimeter on many occasions,” the order said.

The chance disclosure is the first official MND acknowledgement of the facility, which local sources describe as a combined version of the U.S. National Security Agency and National Reconnaissance Office.

Operated by the MND’s Office of Telecommunication Development, General Staff Headquarters, it serves as the primary IMINT/SIGINT center for collecting and processing intelligence about China’s military.

Two flags on the building indicate the facility is under the command of an Army two-star general directly under the authority of the MND. The Marine Corps’ 77th Regiment is responsible for base security.

Defense News visited the Linyuan base twice recently to confirm its location and configuration. The base consists of a processing center equipped with a large satellite dish for IMINT and twin circularly disposed antenna arrays (CDAA), or “elephant cages,” for SIGINT.

Kuo Nai-jih, author of the Chinese-language book, “The Invisible War Between the Taiwan Strait,” said the Linyuan processing center was built in 2000 and went into operation in 2003.

Until then, the MND processed satellite-collected intel at a center in Xindian. Taiwan has only one reconnaissance satellite, the ROCSAT-2, built by EADS Astrium and launched in 2004. There are unconfirmed reports Taiwan has been leasing French, Israeli and U.S. commercial satellites for imagery of China.

The move to Linyuan was meant to reduce redundancy in collecting and processing IMINT from numerous sources, including the MND, National Space Planning Office and the National Central University, a U.S. defense analyst said.

Linyuan’s two antenna arrays “serve as a giant vacuum cleaner that sweeps up Chinese radio signals,” the analyst said.

The “crop circle” configuration is clearly visible on Google Earth at 25 degrees 5 minutes 41.84 seconds north, 121 degrees 23 minutes 40.95 seconds east. The larger of the two is 1,160 feet wide; the smaller one to the northwest is 580 feet wide.

With a range of around 5,000 kilometers, with a bearing accuracy of about 1 degree, the facility can cover the entire Chinese mainland, said Desmond Ball, a signal intelligence specialist and author of the book, “The Ties That Bind.”

However, Ball warns that the relative importance of HF SIGINT activities has declined as the Chinese military has increasingly moved to satellite communications and shielded cyber/net­worked systems.

The array configuration resembles CDAAs used by the former U.S. Naval Security Group, which used two circular arrays, not the three used by U.S. Air Force CDAAs.

“The taller array [antenna poles] is for the lower frequency range within the HF [high-frequency] spectrum, and the shorter array is for the higher portion of the HF spectrum,” a former U.S. National Security Agency technician said.

The size of an antenna is generally related to a fraction or multiple of the wavelengths it is designed to receive. The higher the frequency of a signal, the shorter its wavelength.

“On the CDAA, incoming signals strike the pole(s) nearest the transmitter first,” the former technician said. “A rotating device called a goniometer senses the electric current induced by the received signal and determines the direction from which the signal is coming.”

Some have confused the Linkou CDAA with a previous antenna facility operated by the U.S. Air Force’s 6987th Security Group in the same area until 1977. The United States switched diplomatic relations from Taipei to Beijing in 1979, ending official military relations with Taiwan. The original U.S. base has been demolished.